1. Field of the Invention
The present invention relates to a multiple-beam optical alignment apparatus, e.g., a three-axes laser apparatus used in the constructional industry and including means for minimizing an angle error of diverged, by a beam splitter, beam portions of a primary laser beam
2. Description of the Prior Art
Conventionally, for splitting a primary laser beam into a plurality of divergent beam portions extending at a right angle to each other, a beam splitter and a plurality of mirrors are used. With this arrangement, each separate mirror and the beam splitter should be precisely adjusted and secured in order to achieve the necessary precision of the alignment of the beam portions with respect to each other. In the newest apparatuses, a single beam-splitting prism is used instead of mirrors. The beam-splitting prism, which is produced with a very high precision with respect to the solid angle between the active surfaces, is adjusted, secured, and fixed in a free space or in a housing with only a small tolerated angular deviation. The beam-splitting prism is generally secured with glue. Such alignment apparatuses have a low mechanical stability against thermal or shock-like loads which are usually encountered in a constructional industry.
U.S. Pat. No. 5,617,202 discloses a multiple-beam laser apparatus in which a beam-splitting prism is used for producing two beams at a right angle to each other. To provide for a lateral deviation of secondary beams of a primary laser beam, there are arranged, on a single active surface of the beam splitter, plane-parallel transparent plates which are located in parallel beam paths between a collimator and the beam splitter.
U.S. Pat. No 5,321,717 discloses the use of special prism combinations for focusing of laser beams which also provide for a lateral displacement of the beams.
U.S. Pat. No. 5,341,246 discloses the use of rotatably adjustable, plane-parallel transparent plates for a lateral deflection of laser beams which are directed to prisms.
U.S. Pat. No. 6,118,471 discloses an arrangement of perpendicularly oriented plane-parallel transparent plates in sections of a divergent beam path for producing a phase difference within the beam path.
An object of the present invention is to provide a simple and mechanically stable alignment apparatus in which an angle error of divergent beam portions of a primary beam, which are deflected by a beam splitter, is minimized.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing an alignment apparatus including a radiation source for emitting a primary laser beam, a beam splitter for diverging the primary laser beam into a plurality of divergent beam portions and means for minimizing the angle error of the divergent beam portions and including a collimator located between the radiation source and the beam splitter for focusing the beam portions and directed them to the beam splitter, and spacially oscillatingly adjustable, transparent, plane-parallel plate arranged in a path of the primary laser beam. The spatially pivoting, transparent plane-parallel plate causes a lateral parallel shifting of the beam which, in combination with the located downstream collimator, leads to the angular offset.
The magnitude of the deflection angle depends on the thickness D and refractive index n of the plane-parallel plate, on focus f of the collimator lens, and the plate inclination angle xcex5. The deviation angle xcex1 is determined from the following equation:   α  =                    (                  n          -          1                )            ⁢              D        ·        ϵ              nf  
Because the lateral parallel adjustable beam is diverged behind the collimator, by an adjusting angle at which it is directed to the beam splitter which splits in different beam portions, e.g., in a reflected beam portion and a transmitted beam portion, an adjustment of angular positions between the beam portions becomes possible as a result of doubling of the adjusting angle with respect to the parallel to the adjusting angle, transmittation which takes place upon reflection.
The adjustment of a spacial inclination angle of the transparent plane-parallel plate, because of a resulting small deviation of the primary laser beam, can be effected rather easily. The fixed adjusted position of the plate remains mechanically stable under the action of temperature and shock loads.
The inclined transparent plane-parallel plate introduces into the beam path astigmatism and coma which can lead to deterioration of the wave front aberration of the laser beam. Therefore, the upper limit of the adjusting angle depends on what collimator lens, numerical aperture of the beam portion, and, finally, what optical quality of the ejected beam are required. However, particular in the constructional industry, the advantage of the mechanical stability is preponderant.
Advantageously, the position of the transparent plane-parallel plate with respect to the collimation unit, which is formed of the radiation source and the collimator, is fixed, after the adjustment, with glue that connects the adjacent surface regions.
Advantageously, the beam splitter is formed as a beam-splitting prism formed with a very high precision of the solid angle between the active surfaces. This permits to eliminate separate components and adjusting steps associated with orientations of beam portions.
Advantageously, the transparent plan-parallel plate is made spacially rotatably oscillatingly adjustable. As a result, with the coaxial rotation, with respect to the primary laser beam, of the plate, the degree of freedom of the adjustment remains constant, which facilitates the adjustment.
Advantageously, the transparent plan-parallel plate is fixedly received in a spherical cap which, after adjustment, is fixed with glue with respect to the collimating unit.
Alternatively, the edge of the transparent plane-parallel plate can be formed as a spherical edge fixed with glue in a seat of a calotte shell.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.